Wind-whipped rainclouds formed a low ceiling over the oceanic buttes and basins of south-central Oregon. The usually sundrenched sage darkened in the weather as I walked, my hood pulled up against the grass-bending tug of the northwest breeze. The air smelled richer than it usually does on the dry side of the Cascades, the sagebrush generously giving out scent in exchange for a little moisture. For a time-traveler in the West, stormy weather like this is best. Especially in the strange light before sunset, the landscape becomes spooky, ethereal. You swear you can glimpse the woolly hulks of mammoths grazing the vast, undulating steppe.

Of course, there wasn't any sage out here during the Ice Age. Instead, the now-treeless landscape held scattered groves of Pleistocene pines. You have to use your mind's eye to see both the trees and the mammoths.

The key to time travel is this: Practice wherever you are. Any landscape will do; you just need some idea of what was out there long ago. The Pleistocene is one of the easiest epochs to visit because remnants from that time are still abundant. You can retrace monumental late-Ice Age floods in the Scablands of eastern Washington, or poke along mammoth-crowded refugia in Colorado's Southern Rockies. (At least 13 mammoths were recently excavated near the town of Snowmass.) The main tool you need to carry is an eye for the past.

Rule #1 for would-be time-travelers: Things didn't look quite the same as they do today.

I picked up a chunk of smoke-hearted obsidian. A piece of black volcanic glass with edges slightly chipped, it looked as if it had been shaped by a tool-making creature. I wasn't the first person to see it, or to hold it.

There were humans here at the tail end of the Ice Age. I began to imagine the gracile movements of people wearing animal skins and carrying spears. As I rubbed the slick, vitreous obsidian with my thumb, I scanned the gaping landscape through their eyes, distances trailing away over the curve of the globe.

Rule #2: Although much has changed, not everything has. Flora and fauna may be different, but the shape of the land is still recognizable.

In the tucks and rolls of topography, I could almost make out herds of wild, blunt-nosed horses, even camels. There would have been cheetahs among them, and ancient pronghorn. Bit by bit, an earlier world began to resolve into life around me.

On my most recent visit to the deep past, I started in the town of Paisley, Ore., population 200. The Pioneer Saloon, just down the road from the Forest Service office, serves Alaskan Amber, and the quesadillas aren't half bad. Photographs from as far back as the late 1800s crowd the walls, including a black-and-white one of men on horseback in front of this same saloon. There was even a faded shot of Kenny Rogers, who visited back in the '70s.

The picture I was interested in, however, was one of the most recent. It showed a man in a bandanna, sunhat and daypack. And it was signed: "Dr. Poop."

I went to the bar and asked if that was indeed a picture of the Dr. Poop -- Dr. Dennis Jenkins. A big-boned woman gave a smile, proud to know him personally.

"You just missed him," she said. "He was through here two days ago."

Senior staff archaeologist for the Museum of Natural and Cultural History at the University of Oregon, Jenkins had been excavating paleo-sites in the high desert around Paisley. His controversial findings have reset the archaeological clock, putting original human occupation much further back than was previously thought.

Jenkins' recent work centered on a row of caves five miles north of town. Among thousands of years of human, animal and plant deposits, he found what appears to be a piece of human feces that radiocarbon dating puts at 14,300 years old. If he's correct, this is evidence of some of the first people on the continent, pre-dating the Clovis Culture, once thought to be the earliest settlers. The DNA in this feces carries haplogroups typical of Siberian genes, suggesting its owner came by the Bering Land Bridge.

Another woman and the man who served me my quesadilla heard Jenkins' name and joined the conversation. They told me how to find the caves in a lava-rock point five miles from town. The woman warned me that the alkali road was "slick as snot" in the rain, so I took the back way around the south end of Diablo Rim on a high-clearance, basalt-strewn track several miles east of the caves. I camped in the BLM Diablo Mountain Wilderness Study Area. That night, raindrops and sleet froze like jewels all over my tent, a little taste of the Ice Age.